Method and device for processing iron silicate rock

ABSTRACT

A method is used to process iron silicate rock. At least one component is at least partially removed from the iron silicate rock. At least one component that is different from iron is thus removed from the iron silicate rock. The processed iron silicate rock is used for the production of pig iron or steel. The device for utilizing the processed silicate rock is designed as a device for producing pig iron or steel.

The invention relates to a process for treating iron silicate rock inwhich at least one constituent is at least partly removed from the ironsilicate rock.

The invention also relates to an apparatus for processing treated ironsilicate rock.

Iron silicate rock is at present virtually exclusively mechanicallyutilized. The iron silicate rock is formed as slag in the smelting ofcopper ores.

The iron silicate rock is at present poured, for example, into molds andthe moldings obtained are used for water frontage stabilization.Granulation of the iron silicate rock is likewise already known. Coarsegranulated material is used, for example, as gravel for railroadembankments. Finer granulated material is used in sandblasting.

In terms of its proportions by weight, iron silicate rock consistsessentially of iron, silicon and oxygen. Apart from the iron content,the iron silicate rock also contains secondary elements, for examplecopper, lead, arsenic, nickel and/or zinc.

In the smelting of copper ores (predominantly chalcopyrite), largeamounts of slag are formed. Based on the amount of starting materialcontaining metal of value, the copper industry produces 600 kg of slag/tof ore concentrate, which is about three times the amount of slagcompared to the iron and steel industry.

Slag purification is already carried out worldwide with the main goal ofincreasing/maximizing the copper yield. There are ultimately two processapproaches:

a) Pyrometallurgical—in an electric furnace or in an oil-/gas-firedTeniente furnace. Here, the molten slag is treated by phase gravimetricseparation of the slag/copper matte mixture. A covering of coke(reducing agent) has the main task of avoiding contact of the melt withoxygen.

b) Hydrometallurgical—slag flotation. After solidification of the slag,a milling process is carried out, followed by flotation of the sulfidiccopper particles. A concentrate is formed and this can be recirculatedto the primary process.

The residual copper contents in these processes are about 0.4-0.8% andboth processes are not designed for the metallurgical removal of furtherimpurities. The slag product formed (regardless of whether from apyrometallurgical or hydrometallurgical process) has a problem: there isvirtually no economical use and the available uses have little addedvalue. The greatest part of the copper slag produced worldwide (about 15million t/a) is therefore dumped.

It is an object of the present invention to improve a process of thetype mentioned at the outset in such a way that improved economics areprovided.

This object is achieved according to the invention by at least oneconstituent other than iron being at least partly removed and by thetreated iron silicate rock being used for the production of steel or pigiron.

A further object of the present invention is to construct an apparatusof the type mentioned at the outset in such a way that improvedeconomics are achieved.

This object is achieved according to the invention by the apparatusbeing configured as a facility for producing pig iron or steel.

The metal content of copper slags has hitherto not been utilized(neither the nonferrous metals nor the iron content). At an amount ofslag of 700 kt/a, this corresponds to an iron content of 280 kt/a. Theslag is already liquid and comparatively little additional energytherefore has to be employed in order to carry out the process. Thepresent invention is therefore based on the approach of removing thenonferrous metals from the slag product and using the remaining slagproduct (contains slag formers Si, Ca, Mg, Al and Fe as oxides) and rawmaterial for producing pig iron or steel.

This downstream process allows the preceding process steps moreflexibility in the processing of the copper raw materials. Thecomplexity of these raw materials in respect of their composition willincrease further in future, due to the available copper ore depositsbecoming poorer. Apart from impurities of economic interest (processingsmelters receive a reimbursement from the mines for the processing ofconcentrates having increased contents), e.g. As, Pb, in the steelindustry other important parameters are especially, for example, Zn andsteel contaminants such as S and P. In addition, the copper yield isnaturally critical. The newly developed process of the invention coversthese challenges and pursues the objective of “zero-waste metallurgy”,i.e. all products formed in the production process are processedfurther.

A key-point-type description of the essential process steps for carryingout the treatment according to the invention of iron silicate rock isgiven below.

Process Description

Starting materials:

-   -   Iron silicate rock, fayalite—(Cu slag from primary copper        production)    -   Reducing agent (solid—coke, coal; gaseous—CO, H₂, Fe)    -   Collector metals (Cu, Fe)    -   Electric energy    -   Natural gas or natural gas decomposition products    -   Air/oxygen    -   Circulation products from the copper and steel industry (i.e.        dross, litharges, fly dusts, speise, metal phases) or slags

Process temperature:

-   -   1300-1600° C. (optimal process temperature hitherto 1400° C.)

Plant:

-   -   Electric furnace (rectangular, treatment zone, calming zone,        tapping points configured as overflow, input via channel system,        gas introduction by means of bottom flushing)    -   Closed AOD converter with bottom flushing

Process operation:

-   -   Discontinuous    -   Continuous (preferred, but whether it is actually implementable        depends on ongoing studies)    -   Multistage—necessary!

Energy introduction:

-   -   Electric furnace→electric (very low oxygen potentials can be        set)    -   AOD converter→gas-fired (substoichiometric combustion necessary        (□<1; preferably 0.8-0.9; disadvantage—oxygen potential is        increased compared to an electric furnace)

Residence time:

-   -   Not yet finally determined; about 2-6 h

Products:

-   -   Slag product(s)—fayalite product, magnetite product    -   Fly dust    -   Metal alloy

Illustrative embodiments of the invention are schematically depicted inthe drawings. The drawings show:

FIG. 1: a schematic flow diagram of the process,

FIG. 2: a table showing the specification of the starting material,

FIG. 3: a table showing the specification for the slag product from theprocess.

FIG. 1 shows a schematic depiction for carrying out the individualprocess steps. In particular, the process sequence in the deep reductionof iron silicate rock to give a fayalite or magnetite product as rawmaterial for use in the iron and steel industry is depicted.

The slag from the primary copper process is preferably introduced inliquid form into the deep reduction process. The liquid slag preferablyhas a temperature in the range from 1200° C. to 1350° C. A temperaturevalue of about 1260° C. is typical.

As an alternative, working up slag heaps by the process of the inventionis also envisaged. However, compared to processing of liquid slag, thisinvolves a higher energy consumption since melting of the solid materialis firstly required. A typical analysis of the starting material isshown in the table in FIG. 2.

The objective of the process is to separate the more noble metals ofvalue present from the iron by selective reduction. The iron remains,bound to silicon and/or to oxygen as fayalite product (Fe₂SiO₄) ormagnetite product (Fe₃O₄), for further use as starting material in theiron and steel industry. This product contains further oxides of Ca, Mgor Cr as impurities. The specification for the product is shown in thetable in FIG. 3.

During heating to the preferred process temperature of 1400° C., theresidual sulfur present has to be removed from the system byintroduction of oxygen in order for the subsequent reduction period tobe able to be carried out efficiently. The melt bath is covered andprotected from further contact with oxygen by addition of not more than7% of solid carbon, based on the amount of slag. The CO/CO₂ ratio of theprocess atmosphere should be set so that an oxygen potential of 10⁻¹²atm is not exceeded. In this phase, the volatile constituents of theslag vaporize and leave the process together with the offgas. In thecourse of the offgas treatment, these constituents are obtained in theform of their oxides as fly dust. The fly dust obtained has acomposition of about 40-60% of Zn, 10-20% of Pb and <10% of As and canbe used as raw material for zinc production, e.g. in the rollingprocess. In the example shown here with an annual tonnage of 700 000 t,an amount of fly dust of about 20 000 t is to be expected.

The copper content after this process step is still about 0.2-0.3% ofCu. To separate copper and iron selectively, carbon monoxide isintroduced as reducing agent via flushing bricks arranged at the bottom.The advantage of bottom flushing is the significantly lower gas velocityrequired compared to flushing by means of a lance. This leads tointensive mixing between slag, metal and gas phase. The reduction takesplace at the gas/slag phase interface according to the reaction equationCu₂O+CO→2Cu+CO₂. The metal droplets formed are very fine (max. 20 μm)and have to be separated from the slag phase by density separation in acalming zone.

Depending on the further processing route, the mineralogy of the slagproduct can be matched to the respective use. If the product is, forexample, to be used directly in a blast furnace, the fayalite phaseobtained is satisfactory. For introduction via the blast furnacecharger, pretreatment in the sintering plant is necessary. The meltingrange of fayalite (about 1180°) is too low for this and would lead toproblems in processing. It is therefore necessary to set the magnetitecontent in the finished product. This ratio can be adjusted according tothe requirements of the customer by addition of a defined amount ofoxygen. The oxygen can be added not only in the form of oxygen gas butalso in the form of intermediates which serve as oxygen donors, e.g.Fe₂O₃ dust from the steel industry.

1-11. (canceled)
 12. A process for treating iron silicate rock,comprising the steps of: at least partly removing at least oneconstituent other than iron from the iron silicate rock; and using thetreated iron silicate rock for producing pig iron or steel.
 13. Theprocess according to claim 12, wherein the iron silicate rock is treatedin a liquid state.
 14. The process according to claim 12, wherein theiron silicate rock is treated at a temperature of from about 1300° C. to1600° C.
 15. The process according to claim 12, including introducing areducing agent.
 16. The process according to claim 12, includingcarrying out the treatment in a plurality of stages.
 17. The processaccording to claim 12, including introducing oxygen for at least part ofthe time during treatment.
 18. The process according to claim 12,including carrying out the treatment within an electric furnace withbottom flushing.
 19. An apparatus for treating iron silicate rock,comprising: a furnace that has a feed facility for a gas, the ironsilicate rock being treated in the furnace.
 20. An apparatus forprocessing treated iron silicate rock, wherein the apparatus isconfigured as a facility for producing pig iron or steel.
 21. Theapparatus according to claim 20, the facility is a blast furnace.